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Old 04-05-2008, 10:54 PM   #1
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Calling Electrical Engineers, Seat control module repair

I wanted to revive this thread to see if we all could collectively put our minds together to try and repair our seat control modules.

As the owner of a 2k1 C320 W203, my drivers side seat control went bad. I promptly took it apart and examined it.

Look at the pic. Besides a microprocessor, 3 or 4 capacitors and 7 prominent relay modules, it didn't look all that complicated.

Didn't see any burn marks either.

The 7 relay modules were Siemens V23084-C2001-A403

Look at the pdf datasheet. Using the 12v power from a molex connector off a computer power supply, I tested pins 1 and 2, and 6 and 7 for continuity. I tested 14 (2 per module) points and all made proper clicking noises.

I also applied an ohm meter to each relay module and got a reading of .25

I'm not an electrical engineer, but what else could possibly have gone wrong? Do relay's wear out?

C'mon guys, please help us all out! Those guy's charging $500 for repair are clearly making out like gangbusters.
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Last edited by c320-3216; 04-05-2008 at 11:03 PM.
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Old 04-06-2008, 12:16 AM   #2
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seat modules

replace them both with the updated assys and move on .how much is everyones time worth to make shotgun attempts at repairing a control unit that costs a couple hundred dollars to replace?
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Old 04-06-2008, 01:09 AM   #3
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If the failed part is known, then it might be possible to repair the module. Without that knowledge, then a detailed analysis is required, including a schematic and definition of any custom programmed ICs.

For example, the relay continuity was checked with the relays de-energized. The defect might be in the energized state.

The resistors and transistors could be replaced with an iron, but the ICs require SMT tools.

Remember if the board is damaged by your rework, then the exchange price is no longer valid. Many circuit boards are easily damaged, especially lead-free.

My best guess would be a relay. A "brute force" technique would be to PROPERLY remove the relay, without damaging the PCB. Verify continuity on the NC and open on the NO. Verify the reverse when energized. Do this for both contacts / coils.

Beyond the relay, my next guess would be the relay drive. So check the snubber diode on each coil, forward and reverse diode check. It may work on the PCB. Also check the coil drive transistor. This may also work on the PCB.

Other checks would require documentation, which you'll never get.
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Old 04-06-2008, 08:06 AM   #4
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After re-reading your post, I wouldn't have energized the coil in the board for fear of creating additional damage to other components.

But, since you've already done that, you could possibly repeat that test with lesser risk of inducing additional damage.

So, in addition to measuring continuity on the NC contact, measure open on the NO contact, with the coil de-energized.

Then, with your second set of hands, energize the coil, measure continuity on the NO contact and open on the NC contact.

This testing has the advantage of relay verification without component removal. I would never recommend injecting power onto the coil! But, the author has ALREADY injected power onto the coil. Hopefully any damage from that technique has already been done.

Each coil has a snubber diode that might be able to test in the PCB, forward and reverse. Each coil has a drive transistor that might be able to test in the PCB.
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Old 04-06-2008, 08:11 AM   #5
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The polarity for injecting DC onto the relay coil is critical, or the snubber diode will burn up immediately.
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Old 04-06-2008, 10:29 AM   #6
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just throw caps at it

those caps ar less than a dollar each,use a iron with a pin point tip and "copper" solder wick.watch the polarity on the caps when you r&r.try not to saturate the board with heat when you pull the caps.you will damage the board to some extent,there is no way around it.caps dont have to be the same mf/pf greater values are ok,just not lesser.use the same voltage rating and temp.if the caps dont fix the board than throw it away.caps fail,age use,abuse.also heat is a caps worst enemy,try to install the caps really fast just a momentary application of the iron to the board with solder,dont touch the cap leg with the iron. good luck,caps might work.
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Old 04-06-2008, 01:40 PM   #7
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I agree, the Caps are a componet that will age Just be sure to observe the polarity when you reinstall the new ones..
Another option would be to check with Programa and see if it one they repair it.
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Old 04-06-2008, 10:24 PM   #8
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Quote:
Originally Posted by wingless View Post
If the failed part is known, then it might be possible to repair the module. Without that knowledge, then a detailed analysis is required, including a schematic and definition of any custom programmed ICs.

For example, the relay continuity was checked with the relays de-energized. The defect might be in the energized state.

The resistors and transistors could be replaced with an iron, but the ICs require SMT tools.

Remember if the board is damaged by your rework, then the exchange price is no longer valid. Many circuit boards are easily damaged, especially lead-free.

My best guess would be a relay. A "brute force" technique would be to PROPERLY remove the relay, without damaging the PCB. Verify continuity on the NC and open on the NO. Verify the reverse when energized. Do this for both contacts / coils.

Beyond the relay, my next guess would be the relay drive. So check the snubber diode on each coil, forward and reverse diode check. It may work on the PCB. Also check the coil drive transistor. This may also work on the PCB.

Other checks would require documentation, which you'll never get.
Thanks buddy. FINALLY, someone who has some info. Luckily, this circa 2001 board is not RoHC compliant and doesn't read Pb free so no biggie.

Sorry guys, but i'm an accountant, not an engineer. The relays aren't SMT'ed so I can just solder in new units.

Where/what is a coil drive transistor? Also, when one orders batches of these like 14 (2 seat modules) aren't there usually some defective one's in there? I' already having a difficult time sourcing these puppies nevermind units that have already been tested.

I hooked the seat control module back up the car and it appeared to work as normal with no other kinds/type of damage.
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Old 04-06-2008, 11:22 PM   #9
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Like poster #2 said, you're missing the point that these modules had a design problem and were undated. Why would you bother to fix the version that is guaranteed to fail again?
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Old 04-07-2008, 12:57 AM   #10
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Like poster #2 said, you're missing the point that these modules had a design problem and were undated. Why would you bother to fix the version that is guaranteed to fail again?
Hi, i'm not an engineer, but my thought process is that perhaps MB got a bad batch or relay modules.

Or if there was a design flaw on the circuit board itself, perhaps, newer production run/revision of the Siemens module will be more robust to accomodate say higher voltages or whatever is causing the relay modules to fail prematurely.
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Old 04-07-2008, 06:23 AM   #11
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those caps ar less than a dollar each,use a iron with a pin point tip and "copper" solder wick.watch the polarity on the caps when you r&r.try not to saturate the board with heat when you pull the caps.you will damage the board to some extent,there is no way around it.caps dont have to be the same mf/pf greater values are ok,just not lesser.use the same voltage rating and temp.if the caps dont fix the board than throw it away.caps fail,age use,abuse.also heat is a caps worst enemy,try to install the caps really fast just a momentary application of the iron to the board with solder,dont touch the cap leg with the iron. good luck,caps might work.
If the caps failed they would create a dead short, not a current drain.. also they explode when they fail.

The actual cause really depends on how much current the module is drawing. Before you start changing any components you need to put an ammeter on the module and check its current draw. then you match it up with the various components to see which one might produce that draw if it fails to power down.
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Old 04-07-2008, 09:07 AM   #12
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Quote:
Originally Posted by c320-3216 View Post
Hi, i'm not an engineer, but my thought process is that perhaps MB got a bad batch or relay modules.

Or if there was a design flaw on the circuit board itself, perhaps, newer production run/revision of the Siemens module will be more robust to accomodate say higher voltages or whatever is causing the relay modules to fail prematurely.
Go for it,, If you find the cause great ,, If not you / we learned something. The only thing you risk is the loss of the card. It's only $$ so why not take opportunity. Besides it is already broken so don't think you can break it again. The worst that happens is the card still doesn't work when you finish they you can use it for a paper weight or trotline sinker.

Sometimes it is just fun to take apart and learn,,
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Old 04-07-2008, 04:30 PM   #13
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Like poster #2 said, you're missing the point that these modules had a design problem and were undated. Why would you bother to fix the version that is guaranteed to fail again?
1. I'm a tinkerer at heart.
2. Dealer wants $450+ for part (no core charge)
3. I got time.
4. Times are tough and we throw away enough e-waste as is.

Don't be a hater
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Old 04-07-2008, 07:06 PM   #14
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1. I'm a tinkerer at heart.
Me too, so let us know what you find.

Once I had a caddilac alternator rebuilt 3 times. Each time they told me the regulator (built in check ok and they did not replace it.) Each time it blew the diode assembly. After the third rebuild they told me the problem was in the car. So, I pulled every wire I could find and finally after 12 hrs decided not the car. So I took the alternator back for 4th time and told to rebuild but this time change regulator. They did and gave me the old regulator. Well,, dah,, went 4 years without alternator issues and one day decided to open the regulator, (creramic). After opening I found 1 wire that if broken would cause the alternator to go full output,,, you got it, it was not soldered to the circuit board and when heated up opened the circuit. So I found the problem when even the rebuilder could not. So best of luck you might find something simple. On our Excursion the Fuel mileage indicator goes dim,, we found the resistors where not securly soldered to the board. Soldering them to the board and all was normal. So you might find the answer. Good luck,, Jim
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Old 04-07-2008, 07:59 PM   #15
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Originally Posted by c320-3216 View Post
1. I'm a tinkerer at heart.
2. Dealer wants $450+ for part (no core charge)
3. I got time.
4. Times are tough and we throw away enough e-waste as is.

Don't be a hater
I'm a tinkerer at heart too. Nothing to do with hatin', just making sure you know any fix won't last. And sometimes when these modules go, they take a SAM with them. Luckily when I had a DCM take out a SAM it was all on warranty.
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Old 04-08-2008, 04:55 AM   #16
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The module returned to working normally once replaced. An intermittent problem is likely not caused by a solid-state component failure. So, the drive transistors are likely fine.

It is very likely that the relays are problematic. These are easy to test using an ohm meter, in the energized and de-energized state.

It may be the design improvement was to add snubber diodes to the relay coil, or the relay contact, or both, to limit the inductive voltage spike when turning off. That spike can degrade relay contacts very quickly.

Degraded relay contacts would cause intermittent operation.
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Old 04-08-2008, 06:56 AM   #17
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The module returned to working normally once replaced. An intermittent problem is likely not caused by a solid-state component failure. So, the drive transistors are likely fine.

It is very likely that the relays are problematic. These are easy to test using an ohm meter, in the energized and de-energized state.

It may be the design improvement was to add snubber diodes to the relay coil, or the relay contact, or both, to limit the inductive voltage spike when turning off. That spike can degrade relay contacts very quickly.

Degraded relay contacts would cause intermittent operation.
Possibly a capacitor was added across the relay contacts to minimize contact wear. It would also block dc flow when the contacts are open.
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Old 04-08-2008, 04:50 PM   #18
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I'm a tinkerer at heart too. Nothing to do with hatin', just making sure you know any fix won't last. And sometimes when these modules go, they take a SAM with them. Luckily when I had a DCM take out a SAM it was all on warranty.
Ever see a grown man cry? I appreciate the words of caution since my eyes are almost always bigger than my stomach. MB electronics are wicked expensive to "tinker" on.

My rear SAM got blown before this anyway so I have one on order. i REALLY wish SOMEONE with a post facelift W203 would pop the top off there seat control module tand photograph it to see what revisions Mercedes made from a cursory glance.

Otherwise, thanks everyone for your continued input. I'm going to try and source the modules hopefully as samples rathar than the $15/each quote I got from a vendor.

thanks,
Ben
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Old 04-11-2008, 01:55 AM   #19
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The relays in the assembly are seldom bad. These AMERICAN designed relays by Siemens are very robust on the contact side, while the coil has a time honored winding technique to assure low inrush current, with a rather tame flyback pulse. The drive for most of these relays are surface mount transistors, which inside are the same as through hole transistors made for forty years. They are not the problem either.

The problem with these modules is related to the CANbus. The module has a power supply in the corner with the capacitors. The power supply is "switched off" when the car is turned off, or if the module has not been addressed for a period of time. The processor in the center has a "keep alive" power circuit that just sips current from the battery. When the CANbus wakes up the module, the processor turns on the power supply, and the module draws much more power from the battery.

The failure is when the processor locks up, and does not turn off the power. The power is just enough to make the battery flat rather quickly. The design and use of the processor seems to be the bad actor. Replacing it is not easy. There is software in the processor, so even if you sourced the processor, you would be missing the "operating system." If programmed parts were available from somewhere, the physical task of reworking the assembly is considerable. A couple of grand in equipment is needed to remove and replace the part.

I am not sure if the new processor even has the same pin out, and/or the connections to the I/O are the same.
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Old 04-11-2008, 12:07 PM   #20
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xJ9,are you positive?

Quote:
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If the caps failed they would create a dead short, not a current drain.. also they explode when they fail.

The actual cause really depends on how much current the module is drawing. Before you start changing any components you need to put an ammeter on the module and check its current draw. then you match it up with the various components to see which one might produce that draw if it fails to power down.
are you sure that a failed cap in a circuit will allways create a dead short?.also caps can be bad with no visual clues at all.im under the impression that these caps are added to this pcb to regulate voltage and are quite likely a suspect component,caps,transistors,resistors,diodes,voltag e regulators are all potential repairs that we can do at home.IC's are tough to troubleshoot without an internal diagram and the use of a scope at minimum,and the r&r is quite likely to destroy the board and the new IC if you dont have the right eqip.
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Old 04-11-2008, 03:29 PM   #21
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If the cap fails shorted it will pass DC. If it fails open it will pass nothing. It could fail either way. I have seen them fail and be open. I have also seen them fail and short. But it has been a long time since the oily paper has been used.
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Old 04-11-2008, 03:50 PM   #22
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But it has been a long time since the oily paper has been used.
Really? So I should stop calling them condensors too, I guess.
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Old 04-13-2008, 03:11 PM   #23
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Originally Posted by c320-3216 View Post
1. I'm a tinkerer at heart.
2. Dealer wants $450+ for part (no core charge)
3. I got time.
4. Times are tough and we throw away enough e-waste as is.

Don't be a hater
I told ya' Ben, I can get you a new one for $275 plus around $5 shipping. Why kill yourself.
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Old 04-14-2008, 02:28 PM   #24
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please help

My seat controller is all back to front could anyone help
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Old 04-25-2008, 05:14 PM   #25
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24 posts and only one person knows what they're talking about. the seat control modules themselves do not draw too much current. as stated below, they are keeping the can bus alive.
Quote:
Originally Posted by Moviela View Post
The relays in the assembly are seldom bad. These AMERICAN designed relays by Siemens are very robust on the contact side, while the coil has a time honored winding technique to assure low inrush current, with a rather tame flyback pulse. The drive for most of these relays are surface mount transistors, which inside are the same as through hole transistors made for forty years. They are not the problem either.

The problem with these modules is related to the CANbus. The module has a power supply in the corner with the capacitors. The power supply is "switched off" when the car is turned off, or if the module has not been addressed for a period of time. The processor in the center has a "keep alive" power circuit that just sips current from the battery. When the CANbus wakes up the module, the processor turns on the power supply, and the module draws much more power from the battery.

The failure is when the processor locks up, and does not turn off the power. The power is just enough to make the battery flat rather quickly. The design and use of the processor seems to be the bad actor. Replacing it is not easy. There is software in the processor, so even if you sourced the processor, you would be missing the "operating system." If programmed parts were available from somewhere, the physical task of reworking the assembly is considerable. A couple of grand in equipment is needed to remove and replace the part.

I am not sure if the new processor even has the same pin out, and/or the connections to the I/O are the same.
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Old 04-25-2008, 05:14 PM
 
 
 
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